Example of using the navigator.getUserMedia() API extensions to do screen capturing. Note, this is true screen sharing (e.g. more
than just the browser tab) and not tab content sharing. If you're interested in tab sharing,
Chrome has an experimental defined here.

Note: This app is for demo purposes. Your screen is only displayed to you and not sent to another party in any way.
View the source!

Support: Chrome 26 with "Enable screen capture support in getUserMedia()" turned
on in about:flags or --enable-usermedia-screen-capture flag set.